1. Field of the Invention
The present invention relates generally to computerized cartography. In particular, the present invention is directed to automatically assigning priorities to elements of a map based on properties of those elements.
2. Description of the Related Art
In making maps of states, provinces, countries, or regions, whether by hand or by using a computer program, it is a common practice to display cities as labeled points. Because not all cities are equally significant, cities are prioritized. More important cities—that is, cities that are more likely to be searched for on a map by a wide audience—are displayed and labeled; less important cities are displayed and labeled only where they do not interfere with the display of more important cities. Typically, when cities of various priorities are displayed, the most important cities are displayed with a larger or bolder symbol, and their names are displayed in larger or bolder type, or in all capital letters.
The most common method of assigning priorities to cities is by population. Cities of population greater than some number p1 are shown most prominently; cities with population less than p1 but greater than some number p2 are shown less prominently; cities with population less than p2 but greater than some number p3 are shown still less prominently; and so on, until cities with population less than some number pn are not shown at all.
However, a purely population-based method of assigning priorities is not always optimal. Some cities are important despite having small populations. For example, one typically expects to find a country's capital city on a map that includes that country. The capital of the United States, Washington, D.C., had a population of 572,059 in the 2000 census, making it only the 21st largest city in the United States—smaller than the city of Milwaukee, Wis., the 19th largest city. In spite of Milwaukee's greater population, it would seem odd to find Milwaukee but not Washington labeled on a national map. To account for this, mapmakers often make adjustments to the priorities of cities, in order to make sure that cities that are more important than their populations would imply are displayed appropriately.
A difficulty in making these sorts of adjustments is that the mapmakers require knowledge about the politics and other cultural aspects of the country or region being mapped, and while it is relatively easy to determine that Washington is the capital of the United States, it is less obvious that Las Vegas, Nev. (population 478,434) is significantly more important from a mapping perspective than is Albuquerque, N. Mex. (population 448,607). While both Las Vegas and Albuquerque are approximately the same size, Las Vegas is a major American tourism center (and thus is often searched for on a map), while Albuquerque is not.
Now that an increasing number of maps are being produced using computers, it is desirable to automate the determination of which cities should be included without relying solely on population data and without requiring that the mapmakers have extensive political and cultural knowledge of the area being mapped.